Recent development of networking has created new applications for network communications devices which transmit/receive e-mail messages over the Internet or like network.
Some newly developed network communications devices can not only capture an image with a built-in scanner function, but also forward the captured image information to a computer or like apparatus connected to the network in the form of an attachment to an e-mail message.
Other network communications devices having the same arrangement have also been developed: for example, network scanners (network communications devices) with a “scan to e-mail” function. The function scans an original image for format data to create an e-mail attachment and sends the attachment to an e-mail message to an address (host computer) on the Internet.
Network facsimile machines have been developed too which incorporate a built-in print function and telephone function in addition to the scanner function.
Such a network facsimile machine is disclosed in, for example, Japanese Published Unexamined Patent Application 2001-274944 (Tokukai 2001-274944; published on Oct. 5, 2001). FIG. 10 is a schematic showing an arrangement of a network communications system with such a network facsimile machine.
As shown in the figure, in the network communications system, an e-mail message sent from a transmitting-end terminal machine (network facsimile machine) 101 to a transmitting-end mail server machine 102 is transferred to a receiving-end mail server machine 104 over a network 103 using a predetermined mail transfer protocol such as SMTP (Simple Mail Transfer Protocol). The e-mail message is then stored in the mail server machine 104. A receiving-end terminal machine (network facsimile machine) 105 periodically accesses the receiving-end mail server machine 104 using POP3 (Post Office Protocol 3), IMAP (Internet Message Access Protocol), or another mail receive protocol to retrieve the e-mail message stored there.
Further, the network communications system is adapted to delete the e-mail message received by the terminal machine 105 from the mail server machine 104 so that the e-mail message is not repeatedly transferred after the receiving-end terminal machine 105 receives the e-mail message and prints out the attached image information as a received document.
A problem occurs under these circumstances where information is transmitted using an e-mail message as in the foregoing: unlike, for example, those cases when information is transmitted by an ordinary facsimile machine, the transmitting-end of the network communications system has no means to determine whether the information has been received successfully or processed properly by the receiving-end.
Specifically, unlike ordinary facsimile machines performing real time communications with each other over a PSTN (Public Switched Telephone Network), the receiving-end terminal machine 105 of the network communications system is not always connected to the mail server machine 104, and the transmitting-end terminal machine 101 can forward a message to the mail server machine 102 anytime no matter whether the receiving-end terminal machine 105 can receive it at that time; therefore, the receiving-end terminal machine 105 may take time to actually receive the message. In the event, the transmitting-end terminal machine 101 cannot determine immediately after transmission whether the message has been received successfully or processed properly by the receiving-end terminal machine 105.
Therefore, in conventional network communications systems, when there is a need to verify safe delivery of the transmitted information, the operator must inconveniently confirm it by telephone. It is also a problem that e-mail communications loses an advantage over telephone communications that the parties involved do not need to talk to each other in real time.
Accordingly, another conventional method addressing these shortcomings is defined in the MDN (Message Disposition Notification) method in RFC 2298 which provides a means of confirming safe delivery of an e-mail message whereby upon reception of an e-mail message, the receiving-end terminal machine sends a confirmation message back to the transmitting-end terminal machine.
“RFCs” (Requests For Comments) are official documents issued by the IETF (Internet Engineering Task Force), an Internet-related technology standards body. The documents define, for example, specifications and requirements of Internet protocols, such as IP (Internet Protocol), TCP (Transmission Control Protocol), HTTP (HyperText Transfer Protocol), and FTP (File Transfer Protocol), and various Internet-related technologies. They are numbered throughout like “RFC 2298” and publicly available.
The MDN gives a new “Disposition-Notification-To” field in the header of e-mail messages. The disposition is verified using this field provided that the transmitting-end and receiving-end terminal machines meet the MDN specifications. Specifically, the transmitting end specifies an address in the field to which a disposition verification message should be directed before transmitting the message, and the receiving end sends a disposition verification message to the address specified in the field. The immediately following prior art technology utilizes the MDN function to quickly and reliably deliver an e-mail message to the destination.
Japanese Published Unexamined Patent Application 2001-309109 (Tokukai 2001-309109; published on Nov. 2, 2001) discloses an arrangement of a machine equipped with the MDN function where if the transmitting end sends an MDN request, but does not receive a return message by e-mail from receiving-end within a certain period of time after the completion of the transmission, a disposition failure notice is printed out to notify the operator that no message is sent back. The operator at the transmitting-end terminal machine can thereby confirm whether the message has been successfully transmitted to the receiving-end terminal machine, and retransmit the message or perform another process without delay.
Japanese Published Unexamined Patent Application 2002-32318 (Tokukai 2002-32318; published on Jan. 31, 2002) discloses a communications terminal machine adapted to determine whether an incoming e-mail message includes a disposition verification request and if it does, transmit a disposition verification in the same call as the incoming e-mail message. The arrangement can send a response without delay and at a minimal communications cost.
When the terminal machine receives e-mail messages stored in a mail server machine, it does so in the same order as the mail server machine stores/receives the messages, i.e., by the message numbers. If the terminal machine cannot receive all the messages addressed to that terminal machine in a single connection to the mail server machine due to memory capacity constraints of the terminal machine, the terminal will receive the remaining messages in a next connection.
Therefore, even if the receiving-end terminal machine sends a reply message indicating disposition verification of an e-mail message as quickly as possible, and the mail server machine receives the reply message before a timeout, the transmitting-end terminal machine (the terminal machine which made an MDN request in the first place) may fail to receive the reply message due to its memory capacity constraints, resulting in a timeout error.
In addition, if the MDN indicates a failed delivery, there is usually a need to give priority to receipt of a reply message to MDN over that of ordinary e-mail messages for quick implementation of a retransmission of the e-mail message or another process.